An array antenna MUSIC algorithm is known as a technique of determining an arrival direction of a radio wave using a signal received by a plurality of antennas constituting an array antenna. The MUSIC algorithm uses a mode vector in calculating the arrival direction. The mode vector represents a phase difference or amplitude difference between the antennas as a function of the arrival direction. All the antennas are designed to have uniform and ideal characteristics.
However, the characteristics of the antennas usually become different from each other due to asymmetry of arrangement of the antennas. Particularly, the antennas located on ends of the array antenna have a strong degree of coupling of only the edges thereof with the adjacent antennas, which results in asymmetrical radiation characteristics. Use of the ideal mode vector, therefore, leads to an error in calculating the arrival direction of the radio wave.
In order to alleviate the above problem, Japanese Patent First Publication No. 2007-121165 teaches techniques of correcting a variation in characteristics among the antennas using Cγ components where C denotes a matric representing mutual coupling between the antennas constituting each channel, and Γ denotes a phase difference or an amplitude difference between the channels.